The present invention relates to an operational amplifier.
A capacitor is often connected to an output terminal of an operational amplifier in an MOS analog circuit such as a switched capacitor filter and a charge-equilibrium A/D converter. An operational transconductance amplifier (OTA) is described in detail, for example in "HIGH VOLTAGE GAIN CMOS OTA FOR MICROPOWER SC FILTERS", Vol. 17, No. 4, 19th Feb. 1981, PP. 160-162, ELECTRONICS LETTERS and serves as a low-power consumption circuit which is capable of providing a high voltage gain and a wide frequency bandwidth for a capacitive load and which does not require a phase compensating capacitor.
Recently, the frequency of signals processed by MOS analog circuits increases more and more and the OTA as above is unsatisfactory for signals of frequencies up to the order of 10.sup.6 to 10.sup.8 H.sub.z.
Therefore, the advent of an operational amplifier has been desired which has a high voltage gain and low power consumption for such high frequency signals.